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Deep Sea Drilling Project Initial Reports Volume 22

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Deep Sea Drilling Project Initial Reports Volume 22 26. NANNOFOSSIL BIOSTRATIGRAPHY, LEG 22, DEEP SEA DRILLING PROJECT Stefan Gartner, Jr., Rosenstiel School of Marine and Atmospheric Science, University of Miami, Coral Gables, Florida INTRODUCTION The late Neogene zonation Emiliania huxleyi to Discoa- ster quinqueramus is essentially that proposed by Gartner, Calcareous nannofossils were recovered at every site 1969 (see also Gartner, 1973, for a detailed chronology). drilled during Leg 22. Not all sites, however, yielded The remaining Tertiary zones are compiled chiefly from equally good assemblages, and, at some sites only a small Bramlette and Wilcoxon (1967); Hay et al. (1967); Hay and fraction of the interval cored and drilled yielded calcareous Mohler (1967); Gartner (1969; 1971); Martini and Worsley sediments. In general, the most representative calcareous (1970); Martini (1970; 1971); Roth (1970); and Bukry nannofossil successions were recovered at the shallower (1971). Because many of these zones are used in a slightly sites, particularly those along the crest of Ninetyeast Ridge modified sense, a brief characterization is given below for (Sites 214, 216, and 217). Poorest recovery of calcareous all nannofossil zones used in this volume. nannofossils was from the deepest part of the Indian Ocean, in the Wharton Basin east of Ninetyeast Ridge (Sites 211, 212, and 213). This is not surprising as the last three sites Emiliania huxleyi Zone are all well below 5000 meters, and one site (212) is situated well below 6000 meters. This same site did yield The interval of occurrence of Emiliania huxleyi: This zone calcareous sediments over much of the interval cored, but spans somewhat less than 200,000 years. the section is by no means representative. In fact, this site has a most unusual history of carbonate deposition in that Gephyrocapsa Zone all the calcareous sediments seem to have been transported to this site by currents, and probably none were deposited The interval from the last occurrence of Pseudoemiliania as normal pelagic sediments from the water column above. lacunosa to the first occurrence of Emiliania huxleyi. One site west of Ninetyeast Ridge (215) also was more than 5000 meters deep and only part of the section was calcareous. Finally, the site drilled on the Bengal Fan (218) Pseudoemiliania lacunosa Zone yielded calcareous material throughout the interval cored, but because of the large proportion of detrital constituents, The interval from the last occurrence of Discoaster brou- the calcareous nannofossils and other pelagic constituents weri to the last occurrence of Pseudoemiliania lacunosa. were diluted to such an extent in some parts of the interval that they were only rarely encountered. Discoaster brouweri Zone The interval from the last occurrence of Discoaster surculus NANNOFOSSIL ZONATION to the last occurrence of Discoaster brouweri The top of The calcareous nannofossil zonation used during Leg 22 this zone corresponds very closely to the Pliocene-Pleisto- is indicated below. With the exception of the Discoaster cene boundary as commonly recognized in deep-sea sedi- asymmetricus Zone, all of the zones listed were readily ments. recognized in the sediments recovered in the Indian Ocean. Recognition of the Discoaster asymmetricus Zone depends Discoaster surculus Zone on the identification of Discoaster asymmetricus and Ceratolithus tricorniculatus s.l. in an interval where both The interval from the last occurrence of Reticulofenestra species may be relatively rare, and hence the zone may go pseudoumbilica to the last occurrence of Discoaster undetected in a preliminary examination. Despite this fact, surculus. it has not been excluded from any scheme presented here. Data for constructing the zonal succession and the zonal names are drawn from all available sources. In choosing Reticulofenestra pseudoumbilica Zone from among the various zonations, preference was given to zones which are readily recognized in oceanic as well as in The interval from the last occurrence of nonbirefringent hemipelagic sediments. Provincial species, especially those ceratoliths (chiefly Ceratolithus tricorniculatus and Cerato- restricted to hemipelagic sediments, make poor zonal lithus primus) to the last occurrence of Reticulofenestra markers in oceanic deposits. Notorious among the latter are pseudoumbilica. The top of this zone may be difficult to the mid-Tertiary helicopontosphaeras, pentaliths, holo- determine at times because Reticulofenestra pseudoumbil- coccoliths, Ericsonia subdisticha, and some Miocene astero- ica becomes quite rare and may be represented by only liths (e.g.,Discoaster kugleri). small specimens. 577 S. GARTNER Discoaster asymmetricus Zone The base of this zone also corresponds closely to the last occurrence of Discoaster neohamatus. The interval from the first occurrence of Discoaster asymmetricus to the last occurrence of nonbirefringent Discoaster neohamatus Zone ceratoliths. Discoaster asymmetricus as well as nonbirefrin- gent ceratoliths may be rare in this interval in some types of The interval from the first occurrence of Discoaster pelagic sediment. Consequently, this zone may be difficult neohamatus to the first occurrence of Ceratolithus tricor- to recognize at times. niculatus. For practical purposes this is a total range zone as the last occurrence of Discoaster neohamatus closely corre- Discoaster mohleri Zone sponds to the first occurrence of the genus Ceratolithus. The interval from the first occurrence of Discoaster mohleri Discoaster hamatus Zone to the first occurrence of Discoaster multiradiatus. The interval from the first occurrence of Discoaster Heliolithus kleinpelli Zone hamatus to the first occurrence of Discoaster neohamatus. The interval from the first occurrence of Heliolithus Catinaster coalitus Zone kleinpelli to the first occurrence of Discoaster mohleri. The interval from the first occurrence of Catinaster coalitus Fasciculithus tympaniformis Zone to the first occurrence of Discoaster hamatus. The interval from the first occurrence of Fasciculithus Discoaster exilis Zone tympaniformis to the first occurrence of Heliolithus klein- pelli. The interval from the last occurrence of Sphenolithus heteromorphus to the first occurrence of Catinaster coali- Cydococcolithina robusta Zone tus. This characterization is a poor one because it relies on the absence of two index species. Cyclicargolithus flo- The interval from the first occurrence of Cydococcolithina ridanus and Cyclolithella nitescens both occur within this robusta to the first occurrence of Fasciculithus tympanifor- zone but do not range to the very top of it. The Discoaster mis. Ellipsolithus macellus and Chiasmolithus bidens first kugleri Zone of other authors corresponds to the top of this occur near the bottom of this zone, and the last-named zone, but as Discoaster kugleri is not a cosmopolitan species species enjoys by far the most cosmopolitan distribution of the zone is not included. the three. Unfortunately, early specimens of this species are frequently identified as Chiasmolithus danicus with the Sphenolithus heteromorphus Zone light microscope. The interval from the last occurrence of Sphenolithus Cruciplacolithus tenuis Zone belemnos to the last occurrence of Sphenolithus hetero- morphus. The Helicopontosphaera ampliaperta Zone of The interval from the first occurrence of Cruciplacolithus other authors corresponds to the lower part of this zone. It tenuis to the first occurrence of Cydococcolithina robusta. is not included here because the marker species, Helicopon- In oceanic calcareous oozes the Tertiary record generally tosphaera ampliaperta, generally is not found in oceanic- does not extend below this level, so that sediments of the type pelagic sediments. Cruciplacolithus tenuis zone are underlain by Upper Creta- ceous deposits. Sphenolithus belemnos Zone Ceratolithus rugosus Zone The interval of the total range of Sphenolithus belemnos. The interval from the first occurrence of Ceratolithus Triquetrorhabdulus carinatus Zone rugosus to the first occurrence of Discoaster asymmetricus. The interval from the first occurrence of Triquetrohabdulus Ceratolithus tricorniculatus Zone carinatus to the first occurrence of Sphenolithus belemnos. The species Triquetrorhabdulus carinatus seemingly is The interval from the last occurrence of Discoaster quin- highly susceptible to heavy calcification, which makes queramus to the first occurrence of Ceratolithus rugosus. identification uncertain. Hence, identification of the zone The Miocene-Pliocene boundary falls within this zone. also may be difficult. Discoaster quinqueramus Zone Sphenolithus ciperoensis Zone The interval from the first occurrence of nonbirefringent The interval from the first occurrence of Sphenolithus ceratoliths (including but not limited to Ceratolithus ciperoensis to the first occurrence of Triquetrorhabdulus primus) to the last occurrence of Discoaster quinqueramus. carinatus. 578 NANNOFOSSIL BIOSTRATIGRAPHY Sphenolithus distentus Zone Discoaster diastypus Zone The interval from the first occurrence of Sphenolithus The interval of the total range of Discoaster diastypus. distentus to the first occurrence of Sphenolithus ciperoensis. Discoaster multiradiatus Zone Sphenolithus predistentus Zone The interval from the first occurrence of Discoaster multiradiatus to the first occurrence of Discoaster The interval from the last occurrence of Cyclococcolithina diastypus. formosa to the first occurrence of Sphenolithus distentus. Pre-Tertiary sediments recovered during Leg 22 are
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